Ghrelin deficiency predisposes mice to aging-associated inflammation through compromised gut function and microbiota dysbiosis - PROJECT SUMMARY
A hallmark of aging is chronic, low-grade inflammation, thus coining the term “inflammaging”. Inflammaging is a
highly significant risk factor for both morbidity and mortality in the elderly people. In addition, there is a growing
prevalence of inflammatory bowel disease (IBD), a chronic inflammatory condition of the gastrointestinal tract,
among the elderly population (>65 years of age). Increasing evidence suggest a critical role of gut microbiota
dysbiosis in contributing to the inflammation in aging and in IBD. Ghrelin, a 28 a.a. peptide hormone produced
mainly in the gut, plays multi-faceted roles in nutritional balance, metabolism, and inflammation. Preliminary
data show aged Ghrl-/- mice (18-22 months) exhibit increased adiposity, insulin resistance, gut leakiness, and
susceptibility to muscle atrophy. Remarkably, microbiome analysis reveals an increase in Firmicutes and a
decrease in Bacteriodetes in the gut microbiota composition in Ghrl-/- mice at young age (6 months), prior to
manifestation of age-associated metabolic dysfunction. This change in microbiota composition is reminiscent of
that observed in aging C57BL/6 wildtype mice (3 versus 18 months old). Collectively, these data suggest that
gut microbiota dysbiosis may be a unifying factor contributing to the susceptibility of ghrelin-deficient mice to
aging-associated inflammatory pathologies. The overall objective is to determine how gut barrier function and
microbiota is regulated by ghrelin under different pathological conditions. Pharmacological administration of
ghrelin ameliorates sepsis-induced gut barrier dysfunction; leaky gut and microbial translocation/metabolites
are factors contributing to age-associated inflammation. Hence, the central hypothesis is that ghrelin deficiency
leads to decreased gut barrier function, microbiota dysbiosis and altered metabolites, predisposing the animal
to inflammatory pathologies. To address this hypothesis, the following two specific aims are proposed: 1)
Define the role of ghrelin in gut barrier function, microbiota and inflammation during aging; and 2) Determine
the ability of ghrelin to ameliorate colitis and restore microbiota symbiosis. In Aim 1, gut permeability,
microbiota composition and metabolomics, and inflammatory cytokine levels in Ghrl-/- and control WT mice at 3
and 18 months of age will be assessed. Metabolic function, colon and adipose tissue inflammation in young
and old groups will be characterized, and correlated to microbial changes. In Aim 2, dextran sulfate sodium
(DSS)-induced experimental model of ulcerative colitis will be used to test the efficacy and mechanism of
action of ghrelin in 18 months old C57BL/6 mice. Gut function, plasma analysis and inflammation will be
assessed as in Aim 1, at peak of disease activity and in remission. Fecal microbiota and metabolite will be
mapped longitudinally, covering the progression of active colitis. The integrated approach combining metabolic
phenotyping, inflammatory cytokine profile, gut function, microbiota and metabolomics will provide novel
insights into signature bacterial populations and metabolites in the pathogenesis of aging- and colitis-
associated inflammation.
